


In the Heat of the Moment

by modambrosia



Category: Undertale (Video Game)
Genre: Bara Red, Begging, Dom Red, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Embarrassment, Experienced Red, First Time, Inexperienced Sans, M/M, Masturbation, Mating Cycles/In Heat, Overstimulation, Post-Coital Cuddling, Praise, Red has a big fat donger, Sans has breasts and a vagina in this!!!! just an fyi in case some of yall dont like that, Small Sans, Sorry I just really love given them jelly bodies lol they look so cute, Sub Sans (Undertale), dick in pwussy sex
Language: English
Status: Completed
Published: 2019-01-09
Updated: 2019-01-09
Packaged: 2019-10-07 00:54:59
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,956
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17355905
Author URL: https://archiveofourown.org/users/modambrosia/pseuds/modambrosia
Summary: Sans has to cancel his date with Red, but the phone call leaves Red a bit worried-- he heads over to investigate and finds something entirely unexpected. The two of them end up staying in for the evening instead.





	In the Heat of the Moment

**Author's Note:**

  * For [raza-rays](https://archiveofourown.org/gifts?recipient=raza-rays).



> a gift for raza-rays! sorry it took so long, my whole life like literally blew up and suddenly before I knew it five months passed by ‧º·(˚ ˃̣̣̥⌓˂̣̣̥ )‧º·˚anyways ily and i hope u like the fic!!!

Sans has been sprawled on his bed for an hour now. The sheets beneath him are drenched, soaked through with the sweat that slicks his burning bones. Stars, he feels so _hot_. His body aches, each movement bringing attention back to the itching, buzzing magic within him. Beside his head, his phone chimes. Sans grabs it in a limp hand and yanks it up to his face, hazy eye lights squinting in an effort to read the notifications.

 

_*1 Hour Ago, Text From: Red♡_

_[ ;) good morning ]_

_*37 Minutes Ago, Text From: Red♡_

_[ look at this meme i just found lol  -image.jpeg-]_

 

_*12 Minutes Ago, Text From: Red♡_

_[ u excited 4 2nite? cant wait 2 c u <3 ] _

 

_*4 Minutes Ago, Text From: Red♡_

_[ sans ur bro just called and asked if u talked 2 me yet. he said u r sick? ]_

 

_*1 Minute Ago, Text From: Red♡_

_[ u okay hun? pls answer im worried ]_

_*Just Now, Missed Call From: Red♡_

 

The phone slips out of his grasp and smacks into the arch of his nasal cavity. Compared to the agitated fire in his bones, the dull pain of the metal against his face is a welcome distraction. It continues to ding at him beside his skull, angry little beeps that beg him to reply to his datemate. But how could he? What would he even _say?_

 

“Hey, Red,” Sans croaks out in his empty room, “sorry I have to cancel our cool planetarium date tonight. I’m just so horny that it hurts and even though we haven’t had our first kiss yet, I might beg you to fuck me silly the second you show up!” Just envisioning it brings a furious flush to his cheekbones. He and Red have only been dating for a month or so, but no matter how often Red insists that they can take it slow, he just _knows_ Red wants more. And Sans does, too, but he just...can't. It's too humiliating.

 

Red is so large and powerful and strong, with his deep voice and rugged charm. Just having Red hold his little hand in those massive claws makes Sans’ nonexistent stomach do somersaults, he can't begin to think of what it would be like trying to kiss him, let alone go any _further._ Red would loom over him, overwhelming, imposing...lift him up into his arms like he was lighter than air, press a kiss against his neck...let the hot, wet magic of his tongue lick a stripe up his vertebrae--

 

Sans sobs when he realizes that this train of thought has reawakened the magic he’s been fighting back for hours now. His body has covered itself in plush, glowing magic, and between his legs a puffy little cunt has manifested wet and willing. Sans would laugh at the picture he must paint, if he thought he wouldn’t then immediately start to cry afterwards. Even just the cool air of the room against his clit makes his knees tremble.

 

 _If Red were here, he’d take care of this,_ Sans’ mind offered, entirely unhelpful. _He’d call you beautiful and slide one of those big, thick fingers right inside, curl it up where your own fingers can’t even reach, it’d feel so good, so full, so right--_

 

Just as he was getting to the good part, his phone began to ring. A peek to the side shows Red’s contact photo smirking up at him. Oh, fuck. _Fuck, fuck, fuck_. He reaches up and swipes across the screen with a sticky finger, setting it to speaker phone.

 

_“Sans, babe! Hey!”_

 

…Maybe answering the phone wasn’t a great idea. Thinking about Red was one thing, but _hearing_ that impossibly deep grumble makes his pussy slick itself further with wet.

 

“H...hey, Red. I’m s-sorry I wasn’t answering you...d-didn’t mean to-- ah, uh-- make you worry.”

 

“ _Aw, forget about it, baby,”_ Red croons into his ear, and damn it all, he sounds so fucking _delicious._ Sans has to clench his sheets in an iron grip to keep from touching himself. _“Ya sound like ya don’t feel good...ya need me to come over and make ya feel better?”_

 

_Fucking hell._

 

Any resolve Sans had been using to stop from touching himself was gone in an instant. With one hand gripping the sheets above him, Sans lets the other snake down between his legs to swipe desperately against his swollen clit. He knows there's no point in trying-- it's impossible for him to cum. He’s never been able to get himself through a heat without suppressants, because he could never get himself off alone and didn't have anyone he trusted enough to help him.

 

(Some monsters can manage on their own, can push themselves over into enough climaxes that they force the heat out of their system, but some monsters are too weak. Too submissive to do it on their own. Their bodies rebel against the solitude and refuse to peak without the help of some sort of mate.)

 

(Sans, unfortunately, is one of those monsters.)

 

He curses himself for forgetting to stock up on suppressants, so caught up in the excitement of he and Red’s blossoming relationship that the upcoming date had been nothing more than a passing thought, overlooked in favor of preparing for their date...

 

_“...Sans? Baby, yer breathin' real hard, ya gonna throw up or somethin'? What’s goin' on?”_

 

“A-ah, I just-- I can’t-- I can’t talk right now, I gotta go, sorry, don’t come over, I gotta cancel our plans for tonight, I’msorryIgottagoBYE!”

 

Sans hangs up the phone, Red’s muffled shout of confusion cutting off with a beep. He screams out in frustration and speeds up to a breathtaking pace. At this point his cunt is sore and his wrist is cramping, but he's close, he swears he’s almost there, he can still hear Red in his mind encouraging him, _come on, baby, I know ya can do it, so good fer me, cum fer me, sugar--_

 

“Sans, are ya _aaAAH!_ Fuckin’-- oh my God! I-- _Sans?!”_

 

Sans sits up on the bed in a flash, instantly miles away from orgasm. Across the room, Red is frozen where he had teleported, a cherry blush blooming on his face and his mouth dropped open in shock. They stay like that for a few moments: Sans staring at Red, still dripping sweat and sitting in a pool of his own precum, and Red standing with his back to the door, also sweating profusely now, hands out in front of him like he had been about to reach out for Sans.

 

Red breaks the eye contact for just a second and glances down at the sensitive little breasts Sans’ body had formed. It was fast as lightning, a barely-there glimpse, but it was enough to snap Sans out of his trance. He yanks one arm over his chest and the other down to cover his cunt, knees snapping up and locking together in an attempt at modesty.

 

“Don’t look!”

 

“Shit--! Not lookin’, not lookin’!” Red yelps and smacks his hands over his sockets, immediately cries out from the pain, and then finally throws his hood up and cinches the strings tight enough that his entire head is covered. Sans watches as Red fumbles to tie the strings and feels around the wall of the room until he makes it to the small bean bag chair by his window, flopping himself down into the cushion with a groan.

 

"...Sorry fer comin' in wit'out knockin' first." Sans' Soul thumps at the deep, rough rumble of Red's voice from across the room coming muffled through his hoodie. It forces a high whine out of the back of his throat, and Sans can _feel_ Red's eye lights on him through the hoodie. _Fuck._ From inside his cottony jail, Red starts to huff at the air and crackling sparks of energy roll off of his body in waves.

 

"Babe... _Sans._ Are ya--"

 

"Don't! Don't say it," Sans wails and hugs his body tighter. He feels so naked, knowing that no matter how he covers himself, no matter how Red covers his eyes, the overwhelming essence of his heat still sits heavy in the air. A rumbling growl echoes from Red’s ribcage and Sans’ body responds to the sound like a lit match to gasoline. He keens as the unseen flames lick at his Soul, legs dropping open of their own accord, baring himself to the mate his body so desperately craves.

 

“Why didn’tcha tell me, baby? Ya know I can… I can help ya out with… whatever ya need.” Red’s voice is impossibly deeper and accompanied by a spiced cherry scent filtering into the air. His body has clearly begun to recognize Sans’ heat and respond in turn; Red is shifting uncomfortably where he sits, one hand sneaking down to press into his pants in an effort to relieve some of the ache that has started to throb there.

 

Shame and guilt seep into Sans' gut and settle there, an uncomfortable weight against his Soul. “I was...I’m just so nervous. W-we haven’t even kissed yet, and it’s all so-- so fucking _embarrassing_.” Tears he didn't realize were there begin to stream down his cheekbones, and Sans hiccups around a sob.

 

"Oh, babe, no,” Red croons, one of his hands reaching out for Sans on instinct. "Don't cry, it's okay." Sans reaches out for the comforting embrace before remembering that Red can't see him, encased as he was in the fur trim of his hoodie. It's enough to get a watery laugh from him and he mumbles out, "you can take that hood off now," delighting further in the frantic way Red tears himself out of it. Crimson eye lights immediately lock on Sans, and he has to fight his body's desire to curl up into a ball and hide. Arms still outstretched, Sans manages to stutter out, "C-could you come here and just...just h-hold me for a minute?"

 

Red is up and moving toward the bed before he finishes his sentence; Sans gasps when he's suddenly surrounded in a pleasant warmth, the weight of Red's body against his own soothing some of the ache he's been fighting all day. The larger monster hugs him around his shoulders and waist, pointedly keeping away from any of Sans' sensitive bits in a rare display of self restraint. There's a press of teeth against Sans' skull as Red kisses him, soft whispers of _it's okay_ and _I'm right here_ murmured against the bone. It's nice. It's exactly what Sans needs. It's _perfect._

 

...Until it's not enough.

  
  
Sans whines when his Soul gives an impatient hum, reminding him of the ache between his legs, the coiled tightness in his magic. He refuses to look up at Red and instead buries his face further into Red's chest. Those big hands stay where they are around him, but Sans feels the intent in Red's kisses begin to shift. What started out as chaste pecks slowly turns into longer, lingering kisses, sparking magic against him with every heated brush of contact. Sans dares to let one of his hands slide up to caress Red's jaw, and his Soul stutters when he's given a rumbling growl of approval for his efforts.

  
"Whatever ya need, babydoll," Red whispers. His voice has gone rough around the edges and it makes Sans shiver in anticipation. Instead of answering with words, Sans scoots away from Red and lies back into the pillows at the top of his bed. He covers his breasts with his hands and closes his eyes, too afraid to look at his lover's expression. Red chokes out a quiet 'holy _shit_ ' and then suddenly his little hands are covered with larger ones. Red slowly nudges Sans out of the way, cupping each petite breast in a palm. Sans whimpers at the sensation of Red's rougher bones against his nipples as those claws kneed and roll over the magic.

 

"Fuck, yer perfect. Yer everythin' I ever dreamed of an' more."

 

Sans’ Soul glows brighter with the praise and he peeks from between his hands to sneak a glance at Red; he yelps when he finds those bright red eye lights just inches from his own, quickly returning to the safety behind his little barrier. Red chuckles warmly and it send butterflies adrift in Sans’ belly. A wet warmth against one of his tits has him sucking in a sharp gasp, and Red’s pleased rumble makes him release it with a sigh.

  
“That feel good, baby? Y’want me to keep goin’?”

  
“Oh, stars, yeah,” Sans murmurs, unable to keep from pressing himself up into Red’s mouth. The sensation of Red’s fingers and tongue on his breasts is electrifying and he whimpers and writhes beneath the much larger skeleton. It feels good, _so fucking good,_ and Sans’ voice rises in pitch as the magic in his abdomen coils tighter. Red pinches a nipple and nips into the other at the same time and Sans squeaks with shock as an orgasm rushes through him entirely unexpected. Red gives a muffled noise of surprise but otherwise keeps sucking and tweaking while Sans curls around his head, letting the peak surge through him in waves and moaning wanton with every twitch of his muscles. Once it’s gone through him Sans slumps back on to the bed and Red raises his head a bit, looking up at Sans with an expression nothing short of ravenous.

  
“I-I’m sorry, I didn’t mean to-- to _cum_ so soon, _fuck_ \--” Sans tries to continue his apology but is interrupted by a finger pressed against his teeth. Red shakes his head and leans up the last few inches so that their mouths meet in a skeletal kiss. It’s nothing like the innocent pecks he usually places on Sans’ cheek or hands-- this time, it’s all fangs and tongue, drawing embarrassing noises from Sans whenever Red just happens to find an especially sensitive spot in his mouth. Between licks and sucks, Red mutters,

  
“Don’t ya ever apologize fer feelin’ good, babydoll...that was so fuckin’ _hot..._ can’t believe ya came just from that...stars, yer amazin’…”

 

He’s distracted by Red’s kissing, but he’s not so far gone that he misses the hand that begins to drift down from his breast, over the small swell of his belly, stopping just at his waistline. Claws press into the magic there, enjoying the slight give, before Red lets his thumb swipe just below his belly button. He doesn’t go any lower, just slides it back and forth. It’s a question, a silent, _is this alright? Are you still okay?_

  
He’s never been more embarrassed in his life, but still Sans nods against Red.

  
Given the go ahead, Red slowly lets his hand inch down further and further until he’s cupping Sans’ mound. His fingers quickly get coated in slick, and Sans groans as his face flushes bright. His mouth forms the apology he’d like to give but Red just shushes him with a smile. “It’s okay,” he murmurs while letting the palm of his hand press into Sans’ clit and eliciting a delirious moan from him, “don’t worry, I gotcha.”

 

“I-- oh fuck-- oh, _mmmnn,_ I-- Red, _please--!”_ Red has mercy on him and circles a finger in the slick a few times before sliding it in. It’s just like Sans imagined, thick and rough and _stars, he’s so full,_ and his feet scrabble on the blankets for purchase when he tries to thrust himself down on to the appendage.

 

“Relax, relax! I ain’t mean to tease ya like this, but I gotta get ya prepped.”

 

… 

 

“Prepped?”

 

Red chokes on his spit and Sans almost wishes he hadn’t asked as mortification stings in his chest. In lieu of a verbal response, Red takes one of Sans’ little hands in his grasp and presses it into the crotch of his pants.

  
“ _Holy fucking_ \-- that’s not going inside of me.” That’s not to say Sans doesn’t want it, of course, as just the thought has him squirming with desire, but...whatever _that_ is in Red’s pants, it’s definitely wider around than his forearm and, if his guess is correct, about half as long. No creature should have a cock that ridiculously big. In spite of the short shock of cold down his spine at imagining taking it, Sans looks up at Red with a shit eating grin.

  
“I guess you could say...you’ve got a _monster_ cock.”

 

They meet eyes for just a second before the two of them break down into peals of laughter. Red pauses his ministrations to hunch over onto his knees and Sans laughs so hard that his voice starts to sound a bit wheezy. Once their giggles die down, Sans is still nervous, still embarrassed as hell, but something in the air feels...different, now. Red gives him a look so full of fondness it has him giggling again, looking away and trying to fight the butterflies that look sets off in his belly.

 

 _...actually,_ Sans thinks to himself, _the butterflies might be from the arousal coming back._ Where that first orgasm had offered him sweet reprieve, the relief was apparently short lived; Sans groans and squirms impatiently when he feels familiar heat begin to build back up inside him. It really is unbearable-- how did he hold off this long before breaking down and calling for Red? Speaking of Red, the other seems to have noticed Sans’ issue, having removed his fingers to begin disrobing.

Sans would like to say he tried not to stare, but that would be a bold faced lie. Red grins lecherously as Sans gapes, sockets wide and eyelights blown out as he drinks up every last drop of Red’s figure. He can tell Red wants so badly to poke fun and is grateful when he keeps his thoughts to himself-- Sans is already mortified, he’s not sure he could handle any nudges at his embarrassing situation.

 

When Red lines his cock up against his cunt Sans is certain he’s going to pass out. It’s just so _intimate._ He’s never been this close to anyone before, never let anyone this close to _him_ before, and it’s incredibly daunting. To have so much trust in one monster...Sans never thought he’d see the day. Red’s body has to curl at an interesting angle to properly line up with Sans’ own, but it seems neither of them mind. The closeness is nice; Red enjoys being large enough to completely surround Sans, and Sans loves being totally encompassed by Red’s form. He reaches up and sets his hands against Red’s broad shoulders and Red smiles, soft and sweet, pressing their foreheads together so as to look deep into Sans’ sockets.

 

“‘M gonna make it so good fer ya, baby, gonna make ya feel so fuckin’ _good,”_ Red grunts, breath hot against his face, and that’s all the warning Sans gets before he’s stuffed fuller than he’s ever been before. Sans gasps, back arching up  at the intrusion, and his vision whites out from the uncontrolled _pleasure pleasure pleasure_ rocking him to his core. From the previous orgasm and the prep work, Sans had relaxed enough for Red to hilt in one swift pump of his hips; clearly, _Red_ hadn’t even known he would make it so far in one thrust, if the way his body trembles above him is any indication.

 

Sans isn’t sure why Red stopped. To give Sans a few moments to adjust? To try and take things slow? Whatever it is, it’s unbearable, and Sans grinds his hips as much as Red’s girth will allow as he searches for stimulation. “R-Red, move, please-- _fuck me,”_ he gasps, and that seems to shock Red out of his stupor. The snarl he lets out as he draws his hips back is damn near feral and Sans shrieks when Red immediately snaps his hips forward again, settling into a brutal pace that leaves Sans clinging to Red for dear life.

 

Red’s cock hits spots inside of Sans he never knew existed, every drag against his inner walls a blissful torture. It’s good, it’s _too_ good, and Sans’ face glows bright with embarrassment at the noises forced out of him with every thrust. He bites his tongue in an effort to stifle himself, letting out little aborted whimpers and moans, and Red pauses in his motions to dive in for a deep kiss.

 

“Don’t keep yerself quiet,” he growls after successfully stealing Sans’ breath away. “Lemme hear ya scream, babydoll, wanna hear yer voice...c’mon, don’t hide from me…” Red watches Sans’ face with rapt attention and thrusts again, slow and deep and rough. Even if Sans _had_ wanted to stay silent, it would’ve been a useless endeavor; somehow, going slower made the pleasure build on itself stronger than before, and Sans drops his head back to moan _loud_ into the otherwise quiet room. Red’s satisfied chuckle is enough to bring further heat to his cheeks and he whines, writhing beneath his lover as Red brings them back up to their previous speed.

 

It’s all hazy kisses and endless rocking of their bodies into each other; the room is stifling and the air’s gone thick with the smell of sex, a bit of sunlight filtering into the room through Sans’ blinds to cast beautiful shadows across their bones. Red mumbles to him throughout their coupling, hushed whispers of _beautiful_ and _perfect_ and so many _I love you_ ‘s that Sans is certain he’ll never forget exactly the way it sounds tumbling from Red’s mouth. He reaches his peak countless times but Red holds out for him, continuing to grind into Sans’ cunt and draw more sweet wails and begging from him-- they both know it’s for the best, even though Red’s cum three times and Sans is sobbing by his own seventh orgasm, because this method will bring the quickest end to his heat despite the fact that the pleasure is enough to sting by now.

 

By the time Red deems Sans to be through the next burst of his heat, he’s thoroughly fucked and barely coherent. There isn’t enough energy in his body to speak, but he manages a few dazed coos while Red shifts around the room, cleaning the both of them up and changing out the sheets. The small part of Sans’ brain that isn’t totally fucked out has enough sense to be flustered at how much of a _mess_ they must’ve made, but when Red tucks them both under the covers beside each other, he decides to ignore the feeling until tomorrow when he can at least feel his own legs first.

 

It’s still relatively early in the evening, but considering the activities they’ve just spent hours indulging in, Sans figures it isn’t too strange for them to be settling in for bed a bit sooner than normal-- they’ll need their rest for when his heat comes back around again later. Red’s naked body beside him is warm, and unlike the boiling temperature of his heat earlier, this warmth is enjoyable. Soft, gently caressing his bones, enveloping him in a sense of safety. Sans hums and snuggles in closer.

 

Red curls over Sans, tucking the other’s head under his chin and wrapping his body around him as they begin to drift off. “Love ya,” he mumbles, rumbling out a purr to help soothe Sans deeper into rest. Sans is already asleep, but it’s fine-- Red can feel the contented buzz Sans’ Soul gives off and knows he feels the same.

 

Sans and Red never do make it to the planetarium that night, but neither of them mind. They fuck each other so good that the both of them see stars anyways.

**Author's Note:**

> sorry to everyone messaging me that i havent been responding to. tumblr is basically dead for me and idk if ill make a new one, and human interaction lately has been just too much for me to handle. i wanna try to get back in contact with yall but idk if im in a good enough state for it yet. sorry for disappearing into the void lol
> 
> ily


End file.
